Mask for manufacturing semiconductor devices and method of manufacture thereof

ABSTRACT

The present invention relates to a microminiaturization technique to achieve the miniaturization and higher integration of IC chip and to the improvement of a mask used in its manufacturing process. In other words, the phases of lights transmitted through the mask is controlled within one mask pattern. Specifically, a transparent film is formed in such a manner that it covers a mask pattern along a pattern formed by magnifying or demagnifying the mask pattern or otherwise a groove is formed in a mask substrate. A phase difference of 180° is generated between the lights transmitted through the mask substrate and the transparent film or the groove, causing interference with each light to offset each other. Therefore, the pattern transferred onto a wafer has an improved resolution, being used in the invention.

This application is a continuation application of application Ser. No.07/730,221, filed Jul. 15, 1991, now abandoned which is a continuationapplication of application Ser. No. 07/437,268, filed Nov. 16, 1989, nowU.S. Pat. No. 5,045,417.

BACKGROUND OF THE INVENTION

The present invention relates to a mask for use in photolithography andits manufacturing technique, and particularly to a technique effectivelyapplicable to a mask for use of manufacturing semiconductor integratedcircuit device.

In recent years, very fine elements constituting a circuit, very finewirings and very narrow spaces between the elements and wirings havebeen developed in semiconductor integrated circuit devices.

However, along with such development of the elements and wirings and ofthe spaces between elements and wirings, there arises a problem in thatthe accuracy of mask pattern transfer is lowered when an integratedcircuit pattern is transferred onto a wafer by coherent light.

This problem will subsequently be described with reference to FIGS.24(a)-(d).

When a given integrated circuit pattern formed on a mask 50 shown inFIG. 24(a) is transferred onto a wafer by a method of projectionexposure or the like, the phases of lights each transmitted through eachof a pair of transmission regions P₁, P₂ having light shield region Ntherebetween are identical to each other as shown in FIG. 24(b).Consequently, these interferential lights increase their intensities inlight shield region N located between the above-mentioned pair oftransmission regions P₁, P₂ as shown in FIG. 24(c). As a result, asshown in FIG. 24(d) the contrast of a projected image on a wafer, is notonly lowered, but also the depth of focus becomes shallow, causing thetransfer accuracy of the mask pattern to be considerably lowered.

As a means to counteract these problems, a technique of phase shiftinglithography has been developed, whereby the phase of light transmittedthrough the mask is controlled so as to improve the resolution andcontrast of the projected image. The phase shifting lithographytechnique is disclosed, for example, in Japanese Laid-Open Patent No.173744/1983 and Japanese Laid-Open Patent No. 67514/1987.

In the above-mentioned Japanese Laid-Open Patent No. 173744/1983 thereis described the structure of a mask having a light shield region and apair of transmission regions, wherein a transparent material is arrangedat least in either one of the transmission regions sandwitching thelight shield region therebetween, allowing a phase difference to begenerated between the lights each transmitted through each oftransmission regions at the time of exposure and thus these lights beinginterfered with each other to weaken themselves in the region on a waferwhich should primarily be a light shield region.

The function of the light transmitted through such a mask as above willsubsequently be described with reference to FIGS. 25(a)-(d).

When a given integrated circuit pattern formed on a mask 51 shown inFIG. 25(a) is transferred onto a wafer by the method of projectionexposure or the like, a phase difference of 180° is generated betweenthe phase of light transmitted through a transmission region P₂ havingtransparent material 52 of a pair of transmission regions P₁, P₂ whichhave light shield region N sandwitched therebetween and the phase oflight transmitted through the normal transmission region P₁ as shown inFIGS. 25(b) and (c). Therefore, the lights transmitted through the pairof transmission regions p₁, P₂ interfere with each other to offset themin light shield region N located between these transmission regions P₁,P₂. Consequently, as shown in FIG. 25(d), the contrast of a projectedimage on a wafer is improved. Thus, the resolution and depth of focus isimproved, resulting in a higher accuracy of pattern transfer of the mask51.

Also, in the above-mentioned Japanese Laid-Open Patent No. 67514/1987,there is described the structure of a mask having a light shield regionformed by light shielding film and a transmission region formed byremoving the light shielding film, wherein a fine aperture pattern isformed by removing a part of shielding film and at the same time, aphase shifting layer is provided on either one of the transmissionregion or the aperture pattern, and thus a phase difference is generatedbetween the lights-transmitted through the transmission region and theaperture pattern, preventing the distribution of amplitude of lighttransmitted through the transmission region from being spread in thehorizontal direction.

SUMMARY OF THE INVENTION

Nevertheless, the present inventor has found that the conventionaltechnique disclosed in the above-mentioned Japanese Laid-Open Patent No.173744/1983 has the following problem:

The above-mentioned conventional technique in which a phase differenceis generated between the lights transmitted through the pair oftransmission regions does not has any problem as far as a pattern issimply and unidimentionally arranged in a repetitive manner. However, inthe case that the pattern is complicated as in an actual integratedcircuit pattern, the arrangement of the transparent material may beimpossible, and a problem arises in that sufficient resolution is notobtained at some sections.

For example, in the case of an integrated circuit pattern 53 shown inFIG. 26. If transparent material is arranged in a transmission regionP₂, the resolutions in light shield regions N₁ and N₂ are certainlyimproved. However, if transparent material is arranged in transmissionregion P₁ in order to improve the resolution in light shield region N₃,the lights transmitted through transmission regions P₁, P₂ will have anidentical phase, causing the resolution in light shield region N₂ to belowered. Also, in order to improve the resolution in the light shieldregion N₃, a transparent material should be provided in such atransmission region as the transmission region P₃. Then, the transparentmaterial can be arranged in a part of transmission region P₃. In such acase, however, there appears the reversing of phases in the lightstransmitted through the same transmission region P₃, and an unwatedpattern is formed on a wafer. Consequently, it becomes impossible toimprove the resolution in light shield region N₃.

Furthermore, if the pattern is complicated like an actual integratedcircuit one, the arrangement of transparent material is restricted asmentioned above. This makes it difficult to prepare the pattern data ofthe transparent material. Conventionally, therefore, the pattern of thetransparent material should be produced specially while taking intoconsideration the above-mentioned restriction on the arrangement when amask having means for shifting phase of light is manufactured.

On the other hand, the known technique disclosed in Japanese Laid-OpenPatent No. 67514/1987, whereby an aperture pattern is formed in a lightshield region so as to generate a phase contrast between the lighttransmitted through the aperture pattern and the one transmitted throughthe transmission region, makes it difficult to arrange the aperturepattern, the same as in the case of the above-mentioned publication, ifa pattern is as complicated and extremely fine as an actual integratedcircuit pattern. For example, should the width of pattern of lightshield region become narrower, there arises a problem in that thearrangement of an aperture pattern is difficult.

Furthermore, in this conventional technique, no consideration is givenas to the lowering of light intensity at the corners of transmissionregion which takes place along with a further miniaturization oftransmission region required, resulting in a problem posed in that thecorners of a projected image are rounded.

The present invention is to solve the above-mentioned problems, and theobject thereof is to provide a technique whereby the transfer accuracyof a pattern formed on a mask can be improved.

Another object of the present invention is to provide a techniquewhereby the manufacturing time of a mask having means for shifting phaseof light can be reduced.

Still another object of the present invention is to provide a techniquewhereby the resolution of not only each side of a projected image butalso of each corner thereof can be improved.

Among the inventions to be disclosed in the present application, thosetypical ones will subsequently be described.

Now, the first invention is a mask having light shield and transmissionregions and transferring a given pattern at least by irradiation ofcoherent light locally, wherein a phase shifting portion is formed in apart of the aforementioned transmission region for shifting a phase oflight transmitted, and a phase contrast is generated between the lighttransmitted through the aforementioned phase shifting portion and thelight transmitted through the transmission region where theaforementioned phase shifting portion is not formed, and theaforementioned phase shifting portion is so arranged that theinterferential lights of the aforementioned lights can weaken themselvesin the boundary area of the aforementioned transmission and light shieldregions.

The second invention is the method of manufacturing a mask wherein thepattern data of phase shifting portion can automatically be prepared inaccordance with the pattern data of light shield region.

The third invention is a mask in which light shield and transmissionregions are provided on a mask substrate and a given pattern in the maskis transferred at least by the irradiation of coherent light locally,wherein a groove having a depth to reach the main surface of theaforementioned mask substrate is formed, and simultaneously a phasecontrast is generated between the light transmitted through theaforementioned groove and the light transmitted through theaforementioned transmission region, and a phase shifting groove isformed on the aforementioned mask substrate located below theaforementioned groove so as to allow the interferential lights of theaforementioned lights to weaken themselves at the end portion of theaforementioned light shield region.

The fourth invention is a mask in which light shield and transmissionregions are provided on a mask substrate, and a given pattern istransferred at least by the irradiation of coherent light locally,wherein a groove having a depth to reach the main surface of theaforementioned mask substrate is formed in a part of the aforementionedlight shield region, and a phase contrast is generated between the lighttransmitted through the aforementioned groove and the light transmittedthrough the aforementioned transmission region, and a transparent filmis provided above the aforementioned groove so as to allow theinterferential lights of the aforementioned lights to weaken themselvesat the end portion of the aforementioned light shield region, andsimultaneously, subtransmission regions are formed at the corners of theaforementioned transmission region.

According to the first invention mentioned above, the light transmittedthrough phase shifting portion and the light transmitted through theportion where it is not formed interfere with each other to weakenthemselves at the boundary portion of transmission and light shieldregions so that the bleeding of contour of an image projected on a wafercan be reduced, and the contrast of the projected image can be improvedconsiderably, resulting in a remarkable improvement of the resolutionand depth of focus.

Particularly, in the present invention, no restriction on thearrangement of phase shifting portion takes place no matter howcomplicated the pattern is on the mask. Also, there is no difficulty inarranging the phase shifting portion no matter how narrow the width ofpattern becomes in the light shield region.

According to the second invention mentioned above, the manufacturingtime of mask having means for shifting phase of light can be reducedconsiderably because there is no need for preparing specially anypattern data of transparent film or phase shifting groove.

According to the third invention mentioned above, the light transmittedthrough the groove and phase shifting groove interfere with each otherto weaken themselves, making it possible to reduce the bleeding ofcontour of a projected image and to improve the contrast thereof so thatthe solution and depth of focus can be improved remarkably.

According to the fourth invention mentioned above, the light intensityat the corner of transmission region increases by the arrangement ofsub-transmission region thereat so that not only the resolution at eachside of a projected image but also the resolution at the corner thereofcan be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of the principal part of a mask embodying thepresent invention,

FIGS. 2(a)-(c) are sectional views illustrating the principal part ofthe mask in the respective processes of the manufacture thereof,

FIG. 3(a) is a sectional view of the mask shown in FIG. 1 in a state ofexposure,

FIGS. 3(b)-(d) are diagrams representing the amplitude and intensity ofthe light being transmitted through the transmission region of the mask,

FIG. 4 is a sectional view of the principal part of another maskembodying the present invention,

FIG. 5(a) is a sectional view of the mask shown in FIG. 4 in a state ofexposure,

FIGS. 5(b)-(d) are diagrams representing the amplitude and intensity ofthe light being transmitted through the transmission region of the maskshown in FIG. 4,

FIG. 6 is a sectional view of the principal part of another maskembodying the present invention,

FIG. 7 shows top plan views of the principal part of the mask shown inFIG. 6,

FIG. 8 illustrates the construction of a focused ion beam systememployed in the manufacture of the mask,

FIGS. 9(a) and (b) are sectional views illustrating the principal partof the mask in the respective processes of the manufacture thereof,

FIG. 10 is a flow chart representing the procedures through which thepattern data for a phase shifting groove are,prepared,

FIG. 11(a) is a sectional view of the mask shown in FIG. 6 in a state ofexposure,

FIGS. 11(b)-(d) are diagrams representing the amplitude and intensity ofthe light being transmitted through the transmission region of the maskshown in FIG. 6,

FIG. 12 is a sectional view of the principal part of another maskembodying the present invention,

FIG. 13(a) is a sectional view of the mask shown in FIG. 12 in a stateof exposure,

FIGS. 13(b)-(d) are diagrams representing the amplitude and intensity ofthe light being transmitted through the transmission region of the maskshown in FIG. 12,

FIG. 14 is a sectional view of the principal part of still another maskembodying the present invention;

FIG. 15 is a top plan view of the principal part of the mask shown inFIG. 14,

FIG. 16 is a top plan view of the principal part of a mask showing anexample of pattern data for a groove and a sub-transmission region.

FIG. 17 is a flow chart representing the procedures through which thepattern data for the groove and sub-transmission region shown in FIG. 16are prepared,

FIGS. 18 (a)-(i) are illustrations showing the shapes of the pattern inthe course of forming the pattern for the groove and sub-transmissionregion shown in FIG. 16,

FIG. 19(a) is a sectional view of the mask shown in FIGS. 14 and 15 in astate of exposure,

FIGS. 19(b)-(d) are diagrams representing the amplitude and intensity ofthe light being transmitted through the transmission region of the maskshown in FIGS. 14 and 15,

FIG. 20 is a sectional view of the principal part of still another maskembodying the present invention,

FIG. 21 is a top plan view of the principal part of the mask,

FIG. 22(a) is a sectional view of the mask shown in FIGS. 20 and 21 in astate of exposure,

FIGS. 22(b)-(d) are diagrams representing the amplitude and intensity ofthe light being transmitted through the transmission region,

FIG. 23 is a sectional view of the principal part of still another maskembodying the present invention,

FIG. 24(a) is a sectional view of a conventional mask in a state ofexposure,

FIGS. 24(b)-(d) are diagrams representing the amplitude and intensity ofthe light being transmitted through the transmission region of theconventional mask,

FIG. 25(a) is a sectional view of a conventional mask in a state ofexposure,

FIGS. 25(b)-(d) are diagrams representing the amplitude and intensity ofthe light being transmitted through the transmission region of theconventional mask,

FIG. 26 is a partial top plan view illustrating a part of theconventional mask.

DESCRIPTION OF A PREFERRED EMBODIMENT EMBODIMENT 1

FIG. 1 is a sectional view of the principal part of a mask embodying thepresent invention, FIGS. 2(a)-(c) are sectional views illustrating theprincipal part of the mask in the respective processes of themanufacture thereof, FIG. 3(a) is a sectional view of the mask shown inFIG. 1 in a state of exposure, FIGS. 3(b)-(d) are diagrams representingthe amplitude and intensity of the light being transmitted through thetransmission region of the mask.

Mask 1a shown in FIG. 1 of Embodiment 1 is, for example, a reticle usedat a given process in manufacturing a semiconductor integrated circuitdevice. Also, the original pattern of integrated circuit, which is, forexample, five times its actual dimensions, is formed on the mask 1a ofEmbodiment 1.

Transparent mask substrate (hereinafter referred to simply as substrate)2 constituting mask 1a is made of synthetic quartz glass or the likehaving, for example, a refractive index of 1.47. On the main surface ofsubstrate 2, metal layer 3 of, for example, 500-3,000 Å thick ispatterned in a given shape.

Metal layer 3 comprises, for example, a Cr film so that it willconstitute a light shield region A at the time of exposure. Also, metallayer 3 may be of a laminating construction having chromium oxidelaminated on the upper layer of Cr layer.

Furthermore, the portion where the metal layer 3 has been removedconstitutes a transmission region B, and the original pattern of theintegrated circuit formed on mask 1a comprises of the light shieldregion A and the transmission region B.

In mask 1a of Embodiment 1, transparent film 4a formed in a patternslightly wider than that of the above-mentioned pattern of metal layer 3is provided on mask 1a in such a manner that its part extends over thecontour of metal layer 3 into the transmission region B. Consequently,one transmission region B comprises of the region which is covered bytransparent film 4a and the region which is not covered thereby.

Transparent film 4a is formed, for example, with induim oxide (InOx). Amaterial having a sufficiently high transmittance against substrate 2(at least more than 90% required) as well as an excellent property ofadhesiveness to substrate 2 should be selected as a material fortransparent film 4a. The width of the excessive portion of transparentfilm 4a is approximately 0.5 μm, provided that, for example, the widthof pattern of transmission region B is approximately 2 μm. Given thethickness of transparent film 4a measured from the main surface ofsubstrate 2 is X₁, the refractive index of transparent film 4a is n₁,and the wavelength of light irradiated at the time of exposure is λtransparent film 4a is formed to satisfy the relation of X₁ =λ/[2(n₁-1)]. This relation is maintained in order to generate a phase contrastof 180° at the time of exposure between the light transmitted throughtransparent film 4a and the one through the normal transmission region Bin one transmission region B. For example, if the wavelength λ of lightirradiated at the time of exposure is 0.365 μm (i line) and therefractive index n₁ of transparent film 4a is 1.5, the thickness X₁ oftransparent film 4a measured from the main surface of substrate 2 willbe approximately 0.37 μm. Although not shown in the drawing, analignment mark is provided on mask 1a to align its position with that ofmetal layer 3 when, for example, transparent film 4a is formed

Next, the method of manufacturing mask 1a of Embodiment 1 will bedescribed with reference to FIGS. 2(a)-(c).

First, the surface of transparent substrate 2 made of synthetic quartzclass or the like is ground, and after it is cleaned, metal layer 3 madeof Cr or the like of, for example, approximately 500-3,000 Å is formedon its main surface by sputtering or others as shown in FIG. 2(a).Subsequently, on the metal layer 3, photoresist (hereinafter referred toas resist) 5a of, for example, 0.4-0.8 μm will be coated. Then, afterresist 5a is prebaked, a given portion of 5a is irradiated with electronbeam E by the electron beam exposure method or the like in accordancewith the integrated circuit pattern data with the integrated circuitpattern data of a semiconductor integrated circuit device coded andstored in advance in a magnetic tape which is not shown in the drawing.In the integrated circuit pattern data, the position coordinate, shapeor others are also store.

Next, as shown in FIG. 2(b), the exposed portion of resist 5a, forexample, is removed by a developing solution. Then, the exposed metallayer 3 is removed by etching with day etching method or the like togain the pattern of a given shape.

Subsequently, resist 5a is removed by an exfoliative agent and substrate2 is cleaned. Then, after inspection, as shown in FIG. 2(c), the mainsurface of substrate 2 is covered with transparent film 4a of indiumoxide (I_(n) O_(x)) or others by sputtering method or the like. At thisjuncture, the thickness X₁ of transparent film measured from the mainsurface of substrate 2 is, for example, approximately 0.37 μm.

After that, the upper surface of transparent film 4a is coated withresist 5b of, for example, 0.4-0.8 μm and furthermore, on its uppersurface, an aluminum antistatic layer 6 of, for example, 0.05 μm thickis formed by sputtering method or the like.

Subsequently, the pattern formed on transparent film 4a will betransferred to resist 5b by an electron beam exposure system or the likein accordance with the pattern data of transparent film 4a.

The pattern data of transparent film 4a is automatically formed bymagnifying or demagnifying the light shield region A or transmissionregion B of the above-mentioned pattern data of integrated circuit. Inembodiment 1, for example, the pattern data of transparent film 4a isautomatically formed by thickening the pattern width of light shieldregion A by, for example, approximately 0.5-2.0 μm.

Then, mask 1a shown in FIG. 1 will be produced through the processes ofdevelopment, etching of a predetermined portion of transparent film 4a,removal of resist 5b, cleaning, inspection and others.

In order to transfer the pattern of integrated circuit formed on mask 1aonto a wafer covered with resist by use of the mask 1a thus produced,the following steps will be taken, for example.

Mask 1a and wafer are set on a projection aligner for demagnificationwhich is not shown the drawing, whereby the original pattern ofintegrated circuit on mask 1a is projected on a wafer after it has beenreduced to 1/5 optically, and each time the wafer is sequentially movedstep by step, projection and exposure are repeated so that the patternof integrated circuit formed on mask 1a can be transferred onto theentire surface of the wafer.

Next, the function of Embodiment 1 will be described with reference toFIGS. 3(a)-(d).

In mask 1a of Embodiment 1 shown in FIG. 3(a), a phase contrast of 180°is generated between the light transmitted through transparent film 4aand the one through the normal transmission region B (FIGS 3(b) and (c))in each of transmission regions B of mask 1a when the original patternof a given integrated circuit formed on mask 1a is transferred onto awafer by a projection aligner for demagnification or others.

Here, the lights transmitted through the same transmission region Bhaving reverse phases respectively weaken themselves each other at theboundary area of transmission region A and light shield region B becausetransparent film 4a is arranged around transmission region B. As aresult, the bleeding of a contour of image projected on the wafer isreduced so as to improve the contrast of the projected imageconsiderably. Thus, the resolution and depth of focus will remarkably beimproved (FIG. 3(d)). Also, since light intensity is the square of lightamplitude, the waveform in a negative side is reversed to a positiveside as shown in FIG. 3(d).

In this way, it is possible to attain the following effect according toEmbodiment 1:

(1). While lights are being transmitted through each of the transmissionregions B at the time of exposure, a phase contrast of 180° is generatedbetween the light transmitted through transparent film 4a and the onethrough the region which is not covered with transparent film 4a. Theselights thus transmitted weaken themselves each other at the boundaryarea of light shield region A and transmission region B, making itpossible to reduce the bleeding of contour of image projected on thewafer. As a result, the contrast of projected image is considerablyimproved so that the resolution and depth of focus can be improvedremarkably.

(2). Through (1) mentioned above, more tolerance for exposure can beallowed.

(3). Since a phase contrast can be generated within one transmissionregion B, the arrangement of transparent film 4a is not restricted nomatter how complicated the pattern is on mask 1a. Also, the arrangementof transparent film 4a can be made with ease no matter how narrow thepattern width is in light shield region A. Consequently, the patterntransfer accuracy will never be lowered locally even when a patternformed on mask 1a is highly complicated and fine like the pattern of anintegrated circuit so that the pattern transfer accuracy of the entirepattern formed on mask 1a can be improved remarkably.

(4). The pattern data of transparent film 4a can be obtainedautomatically based on the pattern data of light shield region A ortransmission region B, making it possible to prepare the pattern data oftransparent film 4a in a short period of time and also with ease. As aresult, a remarkable reduction for time required for the manufacture ofa phase shifting mask can be achieved.

EMBODIMENT 2

FIG. 4 is a sectional view of the principal part of another maskembodying the present invention, FIG. 5(a) is a sectional view of themask shown in FIG. 4 in a state of exposure, FIGS. 5(b)-(d) are diagramsrepresenting the amplitude and intensity of the light being transmittedthrough the transmission region of the mask in FIG. 4.

In mask 1b of Embodiment 2 shown in FIG. 4, transparent film 4b isarranged in the vicinity of the central part of transmission region B.

In this case, too, transparent film 4b is formed on substrate 2 in sucha manner that its thickness X₁ will satisfy the relation of X₁ =λ/[2(n₁-1)] so as to generate as shown in FIGS. 5(a)-(d) the phase contrast of180° between the light transmitted through transparent film 4b and theone through the normal transmission region B in each of transmissionregions B, B of mask 1b (FIGS. 5(b) and (c)). These lights thustransmitted will weaken each other themselves each other at the boundaryarea of transmission region B and adjacent light shield regions A, A sothat the bleeding of contour of the image projected on a wafer can bereduced. As a result, the contrast of a projected image can beconsiderably improved, making it possible to improve the resolution anddepth of focus remarkably (FIG. 5(d)).

Also, in this case, the pattern data of transparent film 4b canautomatically be prepared by thinning by a given dimension the width ofa pattern of transmission region B which has been obtained by reversingthe positive pattern data of, for example, an integrated circuit patternto the negative one.

According to Embodiment 2, therefore, the same effects as in theaforementioned Embodiment 1 can be attained.

EMBODIMENT 3

FIG. 6 is a sectional view of the principal part of another maskembodying the present invention, FIG. 7 shows top plan views of theprincipal part of the mask shown in FIG. 6, FIG. 8 illustrates theconstruction of a focused ion beam system, FIGS. 9(a) and (b) aresectional views illustrating the principal part of the mask in therespective processes of the manufacture thereof, FIG. 10 is a flow chartrepresenting the procedures through which the pattern data for a phaseshifting groove are obtainable, FIG. 11(a) is a sectional view of themask shown in FIG. 6 in a state of exposure, and FIGS. 11(b)-(d) arediagrams representing the amplitude and intensity of the light beingtransmitted through the transmission region of the mask shown in FIG. 6.

The mask of Embodiment 3 will subsequently be described with referenceto FIGS. 6 and 7. The crosshatching in FIG. 7 shows the light shieldregion A.

In mask 1c of Embodiment 3, phase shifting groove 7a is formed onsubstrate 2 instead of transparent film 4a of aforementioned Embodiment1 as a means for generating a phase contrast between the lights beingtransmitted through transmission region B at the time of exposure.

Phase shifting groove 7a is arranged around transmission region B. Inother words, phase shifting groove 7a is arranged along the contour ofmetal layer 3. The width of phase shifting groove 7a is approximately0.5 μm if the pattern width of transmission region B is given to be, forexample, approximately 2.0 μm. Then, phase shifting groove 7a is formedto satisfy the relation of d=λ/[2(n₂ -1)] where d is the depth thereof,n₂ is the refractive index of substrate 2, and λ is the wavelength oflight irradiated at the time of exposure. This relation is maintained togenerate a phase contrast of 180° between the phase of light transmittedthrough phase shifting groove 7a and that of light through the normaltransmission region B in the lights being transmitted through each oftransmission regions B at the time of exposure. For example, in casewhere the wavelength length λ of the light irradiated at the time ofexposure is given to be 0.365 μm (i line), the depth d of phase shiftinggroove 7a can be approximately 0.39 μm. Also, although not shown in thedrawing, an alignment mark is provided on mask 1c when, for example,phase shifting groove 7a is formed to align its position with that ofmetal layer 3.

Next, focused ion beam system 8 for use in manufacturing mask 1c will bedescribed with reference to FIG. 8.

Inside ion source 9 installed above the system body, such a dissolvedliquid metal as gallium (Ga) or the like, for example, is contained,though not shown in the drawing. Below ion source 9, withdrawableelectrode 10 is installed, beneath of which is provided the first lenselectrode 11a and the first aperture electrode 12a formed by staticlens. Below aperture electrode 12a, the second lens electrode 11b, thesecond aperture electrode 12b, blanking electrodes 13 for controllingthe on/off of beam irradiation, and then third aperture electrode 12cand deflection electrode 14 are installed.

With the formation of each electrode thus installed, the ion beamemitted from ion source 9 is irradiated under the controls of theabove-mentioned blanking electrodes 13 and deflection electrode 14 ontothe mask 1c which is held by holder 15 with patterns yet to be formedthereon. Then, metal layer 3 or substrate 2 can be processed by etchingwith the ion beam by setting at the time of scanning beforehand itsirradiation time and scanning numbers per unit of pixel of, for example,0.02×0.02 μm.

Holder 15 is installed on the sample stand 16 movable in the directionsof X and Y, and sample stand 16 can be positioned by sample standdriving motor 19 when its position is recognized by laser interferometer18 through laser mirror 17 installed at the side of the sample stand.Also, above holder 15, there is installed secondary ion secondaryelectron detector 20 so that the secondary ion and secondary electrongenerated by a workpiece can be detected. Furthermore, electron shawerradiating member 21 is installed above secondary ion secondary electrondetector 20 to prevent a workpiece from being electrified.

The inside of the processing system set forth above has a structurekeeping itself under vacuum by vacuum pump 22 shown in the drawing belowthe above-mentioned sample stand 16. Also, each of the processingsystems mentioned above is structurally controlled by each of thecontrol members 23-27 installed outside the system body so that theiroperations are controlled, and each of the control members 23-27 is alsocontrolled by controlling computer 33 through each of the interfacemembers 28-32. Controlling computer 33 has terminal 34, magnetic diskunit 25 to record data, and MT deck 36.

Next, the method of manufacturing mask 1c of Embodiment 3 will bedescribed with reference to FIG. 8, FIGS. 9(a) and (b) and FIG. 10.

First, as shown in FIG. 9 (a) , metal layer 3 of, for example, 500-3,000Å is formed by sputtering or the like on the main surface of substrate 2which has been ground and cleaned. Then, mask 1c is held by holder 15 offocused ion beam system 8.

Next, ion beam is charged from ion source 9. This ion beam is convergedby each of the above-mentioned electrodes into a beam diameter of, forexample, 0.5 μm. Then, an ion beam current of approximately 1.5 μA isobtained. Subsequently, this focused ion beam is irradiated onto a givenportion of metal layer 3 in accordance with the pattern data of anintegrated circuit pattern stored beforehand in a magnetic tape of MTdeck 36. Then, metal layer 3 is etched. At this juncture, theirradiation time per pixcel is, for example, 3×10⁻⁶ second, and thescanning numbers are approximately 30. Thus, as shown in FIG. 9(b),metal layer 3 is patterned. The patterning of metal layer 3 may also becarried out by an electron beam exposure method or the Like as in theaforementioned Embodiment 1.

After this, a given quantity of ion beam is irradiated onto thealignment mark provided on mask 1c, which is not shown in the drawing,so as to detect a generated secondary electron by secondary ionsecondary electron detector 20, and the position coordinates arecomputed in accordance with the detection data.

Then, based on the position coordinates of the alignment mark thusworked out, sample stand 16 is moved so that the ion beam can beirradiated onto the location where phase shifting groove 7a is formed.

Next, in accordance with the pattern data of phase shifting groove 7a,the ion beam is irradiated onto substrate 2, which has been exposed bythe pattern formation of metal layer 3, along the contour of metal layerto form phase shifting groove 7a (FIG. 6). At this juncture, the depth,width and others of phase shifting groove 7a can be defined by thefocused ion beam accurately with ease.

The pattern data of phase shifting groove 7a is prepared by a logicarithmetic operation on the pattern data of light shield region A (ortransmission region B) and the pattern data obtainable by magnifying ordemagnifying the pattern data of light shield region A (or transmissionregion B).

For example, as shown in FIG. 10, the pattern data of an integratedcircuit is first prepared through the process of LSI circuit design(step 101a), CAD design data (101b), and Boolen OR (101c), and then thedata is produced by the sizing process (102) for the patted data havingthe pattern width of light shield region A which has been thickened onlyby a given dimension. At the same time, the data for pattern data oftransmission region B are prepared in the process of reverse tone (103)by reversing the positive pattern data of an integrated circuit patterninto the negative one. Then, the pattern data of phase shifting groove7a are automatically prepared (105) by executing AND of these patterndata (104).

Next, after phase shifting groove 7a has been formed, the bottom face ofphase shifting groove 7a formed on mask 1c is flattened by dry etchingwith Gas plasma of for example, Freon (CF₄) or the like. With thisflattening of the bottom face of phase shifting groove 7a, theoperativity of phase of the light being transmitted through this groovecan be improved. In this respect, when the dry etching treatment iscarried out, a gas of Freon or the like is supplied for 20 scc/min tothe inside of a treatment chamber of plasma dry etching, the pressure ofwhich is reduced, for example, to 0.1 Torr.

In this way, mask 1c shown in FIGS. 6 and 7 is manufactured.

Next, the function of mask 1c of Embodiment 3 will be described withreference to FIGS. 11(a)-(d).

Now, when the original of a given integraged circuit pattern on mask 1cshown in FIG. 11(a) is transferred by a method of demagnifyingprojection exposure or the like, a phase contrast of 180° is generated(FIGS. 11(b) and (c)) between the light being transmitted through phaseshifting groove 7a and the one through the normal transmission region Bin each of transmission regions B of mask 1c.

Here, the lights transmitted through the same transmission region Bhaving a reverse phase respectively weaken themselves each other at theboundary area of transmission region B and light shield region A becausephase shifting groove 7a is arranged around transmission region B onmask 1c. As a result, the bleeding of the contour of projected image ona wafer can be reduced, and the contrast of a projected image and depthof focus can be improved remarkably (FIG. 11(d)). Also, since the lightintensity is the square of the light amplitude, the waveform in thenegative side of the light amplitude on a wafer will be reversed intothe positive side as shown in FIG. 11(d).

Thus, the following effects can be attained according to Embodiment 3:

(1). While lights are being transmitted through each of the transmissionregions B at the time of exposure, a phase contrast of 180° is generatedbetween the light transmitted through phase shifting groove 7a and theone through the normal transmission region B. These lights thustransmitted weaken themselves each other at the boundary area of lightshield region A and transmission region B, making it possible to reducethe bleeding of contour of image projected on a wafer. As a result, thecontrast of projected image is considerably improved so that theresolution and depth of focus can be improved remarkably.

(2) . Through (1) mentioned above, more tolerance for exposure can beallowed. p1 (3). Since a phase contrast can be generated within onetransmission region B, the arrangement of phase shifting groove 7a isnot restricted. Also, the arrangement of phase shifting groove 7a is notdifficult no matter how narrow the pattern width is in light shieldregion A. Consequently, the pattern transfer accuracy will never belowered locally even when a pattern formed on mask 1c is highlycomplicated and fine like the pattern of an integrated circuit so thatthe pattern transfer accuracy of the entire pattern formed on mask 1ccan be improved remarkably.

(4). The pattern data of phase shifting groove 7a can be obtainedautomatically based on the pattern data of light shield region A ortransmission region B, making it possible to prepare the pattern data ofphase shifting groove 7a with ease and reduce its preparation timeconsiderably.

(5). Since a means for shifting phase of light can be phase shiftinggroove 7a instead of the transparent film as in the aforementionedEmbodiments 1 and 2, the process of forming transparent film is nolonger needed when mask 1c is manufactured.

(6) In addition to the above-mentioned (4) and (5), phase shiftinggroove 7a can also be formed when the patterning of metal layer 3 iscarried out by focused ion beam, so that the mask manufacturing processcan be simplified as compared with the one using transparent film asmeans of shifting phase, and its manufacturing time can be reducedconsiderably.

(7). Since the manufacturing process of phase shifting mask can besimplified, exterior defects, adhesion of foreign materials, or anyothers are prevented effectively as compared with the mask usingtransparent film as means for shifting phase of light.

(8). In case of using phase shifting groove 7a, there is nodeterioration of, for example, the quality of film, transmission rate,or adhesiveness to substrate 2 due to irradiation light or exposurelight after the mask manufactured as in the case of using transparentfilm for phase shifting.

(9). Through (8) mentioned above, the life of mask can be prolonged ascompared with the mask using transparent film as means for shiftingphase of light.

(10). Through (8) mentioned above, the accuracy of phase operation oflight can be maintained longer than the mask using transparent film asmeans for shifting phase of light.

(11). In case of phase shifting groove 7a, there is no need ofconsideration for any deterioration of the quality of film and others asin the case of using transparent film as means for shifting phase oflight. Consequently, such treatment as ozone sulfuric acid cleaning at ahigh-temperature or high pressure water scribble cleaning or others canbe conducted for mask 1c.

(12). Through (11) mentioned above, a removal treatment of foreignmaterials can be conducted better than the mask using transparent filmas means for shifting phase of light.

EMBODIMENT 4

FIG. 12 is a sectional view of the principal part of another maskembodying the present invention, FIG. 13(a) is a sectional view of themask shown in FIG. 12 in a state of exposure, FIGS. 13(b)-(d) arediagrams representing the amplitude and intensity of the light beingtransmitted through the transmission region of the mask shown in FIG.12.

In mask 1d of Embodiment 4 shown in FIG. 12, phase shifting groove 7b isarranged in the vicinity of the central part of transmission region B.

In this case, too, phase shifting groove 7b is formed on substrate 2 insuch a manner that its depth d will satisfy the relation of d=λ/[2(n₂-1)] so as to generate as shown in FIGS. 13(a)-(d) the phase contrast of180° between the light transmitted through phase shifting groove 7b andthe one through the normal transmission region B in each of transmissionregions B, B of mask 1d (FIGS. 13(b) and (c)). These lights thustransmitted will weaken themselves each other at the boundary area oftransmission region B and adjacent light shield region A, A so that thebleeding of contour of the image projected on a wafer can be reduced. Asa result, the contrast of a projected image can be considerablyimproved, making it possible to improve the resolution and depth offocus remarkably (FIG. 13(d)).

Also, in this case, the pattern data of phase shifting groove 7b canautomatically prepared by thinning by a given dimension, the width of apattern of transmission region B obtainable by reversing the positivepattern data of, for example, an integrated circuit pattern to thenegative one.

According to Embodiment 4, therefore, the same effect as in theaforementioned Embodiment 3 can be attained.

EMBODIMENT 5

FIG. 14 is a sectional view of the principal part of still another maskembodying the present invention, FIG. 15 is a top plan view of theprincipal part of the mask shown in FIG. 14, FIG. 16 is a top plan viewof the principal part of a mask showing an example of pattern data for agroove and sub-transmission region, FIG. 17 is a flow chart representingthe procedures through which the pattern data for the groove andsub-transmission region shown in FIG. 16 are prepared, FIGS. 18(a)-(i)are illustrations showing the shapes of the pattern in the course offorming the pattern for the groove and sub-transmission in FIG. 16, FIG.19(a) is a sectional view of the mask shown in FIGS. 14 and 15 in astate of exposure, FIGS. 19(b)-(d) are diagrams representing theamplitude and intensity of the light being transmitted through thetransmission region of the mask shown in FIGS. 14 and 15.

The mask 1e of Embodiment 5 will subsequently be described withreference to FIGS. 14 and 15.

In mask 1c of Embodiment 5, a plurality of grooves 37 which extendrespectively from the top surface of metal layer 3 to the main surfaceof substrate 2 are arranged on the metal layer comprising light shieldregion A.

Groove 37 is, as shown in FIG. 15, is arranged in parallel along eachside of transmission region B in such manner that it surrounds each ofrectangular transmission regions B, B. The width of groove 37 is, forexample, approximately 0.5 μm.

Above groove 37, there is provided transparent film 4c made of indiumoxide (I_(n) O_(x)) or the like having, for example, a refractive indexof 1.5.

With transparent film 4c, mask 1e is so constructed that it generates aphase contrast between the light transmitted through transparent film 4cand groove 37 and the one through transmission region B at the time ofexposure.

Given the thickness of transparent film 4c measured from-the mainsurface of substrate 2 is X₂, transparent film 4c is formed, as in theaforementioned Embodiment 1, to satisfy the relation of X₂ =λ/[2(n₁-1)]. This relation is maintained in order to generate a phase contrastof 180° between the phase of light transmitted through transparent film4c and groove 37 and the phase of one through transmission region B inthe lights irradiated onto mask 1c at the time of exposure. For example,in case where the wavelength of light λ irradiated at the time ofexposure is 0.365 μm (i line), the thickness X₂ of transparent film 4cmeasured from the main surface of substrate 2 can be approximately 0.37μm.

Furthermore, in Embodiment 5, as shown in FIG. 15 rectangularsub-transmission region C of, for example, approximately 0.5×0.5 μm indimension is arranged at each of four corners of rectangulartransmission region B. This is provided in order to prevent the fourcorners of a pattern of an integrated circuit formed at the right angleson a mask 1e from being rounded after its development as theminiaturization of an integrated circuit pattern further advances. Inother words, sub-transmission regions C are arranged respectively ateach of the four corners in an integrated circuit pattern in order toincrease the light intensity in the vicinity of the four corners, wherethe light intensity tends to be most weakened resulting in a greaterdistortion, so that a projected image can be compensated. Also, althoughnot shown in the drawing, when, for example, groove 37 or transparentfilm 4c is formed, an alignment mark is provided on mask 1c to aligntheir position and that of metal layer 3.

To manufacture such a mask as mask 1e, the subsequent procedures will betaken, for example.

First, on the main surface of substrate 2 which has been ground, metallayer 3 of, for example, approximately 500-3,000 Å is formed bysputtering or others. Subsequently, this substrate is held on holder 15of focused ion beam system 8 described in the aforementioned Embodiment3.

Next, metal layer 3 on the main surface of substrate 2 is patterned byfocused ion beam in accordance with the data of an integrated circuitpattern stored beforehand in the magnetic tape of MT deck 36.

Likewise, after this, groove 37 is formed on metal layer 3 byirradiating the focused ion beam onto metal layer 3 on the main surfaceof substrate 2 in accordance with the pattern data of groove 37 andsub-transmission region C stored beforehand in the magnetic tape of MTdeck 36.

The pattern data of groove 37 and sub-transmission region C, as will bedescribed later, can automatically be prepared by providing anarrangement rule against rectangular transmission region B.

Then, the pattern data of transparent film 4c is prepared in accordancewith the pattern data of an integrated circuit pattern and those ofgroove 37 and sub-transmission region C. Based on this, transparent film4c is formed on mask 1c in the same manner as in the aforementionedEmbodiment 1.

Here, the method of preparing the pattern data of groove 37 andsub-transmission region C formed on an integrated circuit pattern shownin FIG. 16 as an example will be described along the flow chart shown inFIG. 17 with reference to FIGS. 18(a)-(i). To facilitate examining thedrawings, however, transparent film 4c is not shown in FIG. 16 Also,crosshatchings in FIGS. 18(a)-(i) represent the patterns produced ineach process respectively.

First, the data of pattern 38 in transmission region B as shown in FIG.18(a) are prepared (steps 101a-101c) through the processes of LSIcircuit design, CAD design, and Boolean OR.

Subsequently, as shown in FIG. 18(b), pattern 39 is defined (102a) bythickening the pattern width of transmission region B by, for example,approximately 2.0 μm through the process of sizing 1.

At the same time, through the process of sizing 2, pattern 40 isproduced (102b) by thickening the pattern width of transmission region Bby, for example, by 1.0 μm as shown in FIG. 18(c).

Next, through the process of corner clipping, the data of pattern 41having only the corners extracted from pattern 39 are prepared a shownin FIG. 18(d) (103a). Then, through the process of reversing tones, thedata of pattern 41 thus prepared are reversed from positive to negativein order to prepare the data of pattern 42 as shown in FIG. 18(e)(104a).

Furthermore, on the other hand, through the process of reversing tones,pattern 40 produced in the above-mentioned process of sizing 2 isreversed form positive to negative, and the data of pattern 43 shown inFIG. 18(f) are prepared (103b).

Then, the data of pattern 44 for groove 37 as shown in FIG. 18(g) areprepared (105a and 106a) by executing AND of the data of patterns 39,42, and 43 shown respectively in FIGS. 18(b), (e) and (f).

Meanwhile, the data of pattern 45 shown in FIG. 18(h) are prepared(104b) by executing AND of the data of pattern 40 shown in FIG. 18(c)and those of pattern 41 shown in FIG. 18(d).

Subsequently, the area b of pattern 45 thus produced is judged to see ifit is smaller than 1/2 of the area a of pattern 41 (105b). Through thisjudgment, those patterns, the area b of which are smaller than 1/2 ofthe area a are selected, and the data of pattern 46 of sub-transmissionregion C shown in FIG. 18(i) are prepared (106b). The reason why thearea of pattern 45 is compared with a given value is thatsub-transmission C region should necessarily be added only to the cornersection having shape of pattern 38 in transmission region B.

Next, the function of Embodiment 5 will be described with reference toFIGS. 19(a)-(d).

When the original of a given integrated circuit pattern on mask 1c shownin FIG. 19(a) is transferred onto a wafer by the method of demagnifyingexposure or the like, a phase contrast of 180° is generated between thelight transmitted through transparent film 4c and groove 37 and the onethrough transmission region B (FIGS. 19(b) and (c)) in each oftransmission regions B in mask 1c.

Here, the light transmitted through transparent film 4c and groove 37and the one through transmission region B weaken themselves each otherat the end portion of night shield regions A, A adjacent to transmissionregion B. Therefore, the bleeding of contour of the image projected on awafer can be reduced to improve the contrast of the projected imageconsiderably, so that the resolution and depth of focus can be improvedremarkably. Now, since the light intensity is the square of the lightintensity, the waveform in the negative side of light amplitude on awafer is reversed to the positive side as shown in FIG. 19(d).

In this way, the following effects can be attained according toEmbodiment 5:

(1). While lights are being irradiated onto mask 1e at the time of,exposure, a phase contrast of 180° is generated between the lighttransmitted through transparent film 4c and groove 37 and the onethrough transmission region B. These lights are made to weakenthemselves each other at the end portion of light shield region A,making it possible to reduce the bleeding of contour of the imageprojected on a wafer. As a result, the contrast of the projected imagecan be improved considerably so that the resolution and depth of focuscan be improved remarkably.

(2). Through (1) mentioned above, more tolerance for exposure can beallowed.

(3). Through (1) mentioned above, the accuracy of pattern transfer canbe improved.

(4). The accuracy of pattern transfer can be improved more by providingsub-transmission region C at each of four corners of transmission regionB because its provision allows the light intensity of the projectedimage there to be further intensified.

(5). The time required for manufacturing phase shifting mask canconsiderably be reduced as compared with the previous one beautomatically producing the patterns of groove 37 and transparent film4c.

EMBODIMENT 6

FIG. 20 is a sectional view of the principal part of still another maskembodying the present invention, FIG. 21 is a top plan view of theprincipal part of the mask, FIG. 22(a) is a sectional view of the maskshown in FIGS. 20 and 21 in a state of exposure, FIGS. 22(b)-(d) arediagrams representing the amplitude and intensity of the light beingtransmitted through the transmission region.

Mask 1f of Embodiment 6 will subsequently be described with reference toFIGS. 20 and 21.

In mask 1f of Embodiment 6, phase shifting groove 7c is formed onsubstrate 2 located below groove 37 instead of transparent film 4c ofthe aforementioned Embodiment 5 as means for generating a phase contrastbetween the light transmitted through groove 37 and the one throughtransmission region B.

Given the depth of phase shifting groove 7c is d, the refractive indexof substrate 2 is n₂ and the wavelength of exposure light is λ, thephase shifting groove 7c is formed to maintain the relation of d=λ/[2(n₂-1)] as in the aforementioned Embodiment 3.

For example, in case where the wavelength of light λ is 0.365 μm (iline) the depth d of phase shifting groove 7b can be approximately 0.39μm.

The bottom face of phase shifting groove 7c is almost flattened by aplasma dry etching treatment as in the aforementioned Embodiment 3 inorder to improve the operativity of light transmitted through the endface thereof. Phase shifting groove 7c is produced by etching substrate2 to the depth d by increasing the scanning numbers of focused ion beamwhen, for example, groove 37 is formed.

Also, in Embodiment 6 as in the aforementioned Embodiment 5, rectangularsub-transmission region C of, for example, approximately 0.5×0.5 μm isarranged at each of the four corners of rectangular transmission regionB as shown FIG. 21. Furthermore, although not shown in the drawing, thealignment mark is provided on mask 1f in order to align its positionwith that of metal layer 3 when, for example, groove 37 orsub-transmission region C is formed.

The pattern data of groove 37 and sub-transmission region C are preparedin the same way as, for example, in the aforementioned Embodiment 5.Also, in this case, the pattern data of phase shifting groove 7c areidentical to those of groove 37.

Next, the function of Embodiment 6 will be described with reference toFIGS. 22(a)-(d).

When the original of a given integrated circuit pattern on mask 1f shownin FIG. 22(a) is transferred onto a wafer by the method of demagnifyingexposure light or the like, a phase contrast of 180° is generatedbetween the light transmitted through groove 37 and phase shiftinggroove 7c and the one through transmission region B (FIGS. 13(b) and(c)).

Here, the light transmitted through groove 37 and phase shifting groove7c and the one through transmission region B in the lights irradiatedonto mask 1f weaken themselves each other at the end portion of lightshield regions A, A adjacent to transmission region B. As a result, thebleeding of contour of the image projected on a wafer can be reduced toimprove the contrast of the projected image considerably so that theresolution and depth of focus can be improved remarkably (FIG. 22 (d)) .Also, since the light intensity is the square of the light amplitude,the waveform in the negative side of the light amplitude on a wafer isreversed to the positive side as shown in FIG. 22 (d).

As set forth above, in Embodiment 6, the following effects can beattained in addition to the effects (1)-(5) of the aforementionedEmbodiment 5:

(1). There is no need for the process of forming any transparent filmfor use in phase shifting, when mask 1f is manufactured because phaseshifting groove 7c is employed instead of transparent film 4c as meansfor shifting phase of light.

(2). In addition to (1) mentioned above, phase shifting groove 7c can beproduced when groove 37 is formed on metal layer 3 by focused ion beam,whereby the process of manufacturing phase shifting mask can besimplified as compared with mask 1e as in the aforementioned Embodiment5, and the time required for its manufacturing can be reducedremarkably.

(3). The manufacturing process of phase shifting mask can be sosimplified that external defect, adhesion of foreign materials, or anyother causes of damage will be prevented remarkably as compared withmask 1e of the aforementioned Embodiment 5.

(4). In case of phase shifting groove 7c, there is no deterioration of,for example, the quality of film, the transmission rate, or adhesivenessto substrate 2 due to irradiation light or exposure light after themanufacture of mask as in the case of transparent film for use in phaseshifting.

(5). Through (4) mentioned above, the life of mask can be prolonged morethan the one using transparent film as means for shifting phase oflight.

(6). Through (4) mentioned above, the accuracy of light phase operationcan be maintained longer than the mask using transparent film as meansfor shifting phase of light.

(7). In case of phase shifting groove 7c, there is no need for suchconsideration as required for deterioration of the quality of film,transmission rate, or adhesiveness, and the removal of film or others asin the case of using transparent film as means for shifting phase oflight. Consequently, ozone sulfuric acid cleaning or high pressure waterscrabble cleaning or other treatment can be conducted against mask 1f ata high-temperature.

(8). Through (7) mentioned above, the removal treatment of foreignmaterials can be conducted better than the mask using transparent filmas means for shifting phase of light.

EMBODIMENT 7

FIG. 23 is a sectional view of the principal part of still another maskembodying the present invention.

In mask 1g of Embodiment 7 shown in FIG. 23, phase shifting groove 7d isproduced at least on either one of a pair of transmission regions B, Bhaving light shield region A therebetween.

The bottom face of phase shifting groove 7d is almost flattened byplasma dry etching treatment as in the aforementioned Embodiment 3 inorder to improve the operativity of phase of light transmitted throughit.

Embodiment 7 is applicable to the portion where an integrated circuitpattern is simply arranged as in the case of, for example, a memorycell.

Phase shifting groove 7d is produced by etching substrate 2 to the depthd by increasing beam scanning numbers when, for example, transmissionregion B is formed as in the aforementioned Embodiment 6, by etchingmetal layer 3 with focused ion beam.

As set forth above, the following effects can be attained according toEmbodiment 7:

(1). At the time of exposure, the phase contrast of 180° is generatedbetween the lights each transmitted through each of transmission regionsB of the pair of transmission regions B, B having light shield region Atherebetween so that the lights each transmitted through each oftransmission regions B having shield region A therebetween can weakenthemselves each other in light shield region A. Consequently, theresolution of an image in light shield region located between-the pairof transmission regions B can be improved, making it possible to improvethe accuracy of pattern transfer.

(2). There is no need for the process of forming transparent film in themanufacture of mask 1g because of phase shifting groove 7d beingemployed as means of shifting phase of light instead of the conventionaltransparent film.

(3). In addition to (2) mentioned above, the manufacturing process ofphase shifting mask can be more simplified than the conventional one,and its manufacturing time can also be reduced considerably by producingphase shifting groove 7d simultaneously with the patterning of metallayer 3 by focused ion beam.

(4). Since the manufacturing process of phase shifting mask issimplified, external defect, adhesion of foreign materials or any othercauses of damage can be prevented remarkably.

(5). In case of phase shifting groove 7d, there is no deteriorations of,for example, the quality of film, transmission rate, or adhesiveness byirrdiation light or exposure light after the manufacture of mask as inthe case of using transparent film for conventional phase shifting.

(6). Through (5) mentioned above, the life of mask having a means forshifting phase of light can be prolonged more than the convention one.

(7) . Through (5) mentioned above, the accuracy for light phaseoperation can be maintained longer than the conventional one.

(8). Since phase shifting groove 7d does not require any considerationfor deteriorations of the quality of film, transmission raze oradhesiveness and the removal of film or others, ozone sulfuric acidcleaning or high pressure water scrabble cleaning or other cleaningtreatment can be conducted against mask 1g at a high-temperature.

(9). Through (8) mentioned above, removal of foreign materials can beconducted better than the mask using transparent film.

As set forth above, the invention of the present inventor has beenspecifically described in accordance with embodiments. The presentinvention, however, is not limited to the aforementioned embodiments,and it is needless to say that modifications and variations are possiblewithout departing from the spirit and scope of the present invention.

For example, in the aforementioned embodiment 3, there is described thecase where the pattern data of phase shifting groove is prepared byexecuting AND of the pattern data obtainable by magnifying the patternof light shield region and the pattern data of transmission region. Itis not limited to this case, and various modification are possible. Forexample, it can be obtained by deducting the original pattern of lightshield region from the pattern formed by magnifying the pattern of lightshield region.

Also, in the aforementioned embodiment 1, 2, and 5, there is describedthe case where the transparent film employed is of induim oxide. Thecase is not limited to the application thereof. For example, silicondioxide, silicon nitride, magnesium fluoride or polymethyl methacrylateor the like can be applied.

The descriptions set forth above have been made chiefly as to theapplication of the invention by the present inventor to the mask used inthe process of manufacturing semiconductor integrated circuit devicewhich is the industrial field defining the background of the invention.The present invention, however, is not limited to such an applicationonly. It may be applicable to various technical fields where a transferof a given pattern to a given substrate is required.

The typical effects obtainable by the invention disclosed in the presentapplication will subsequently be described briefly.

According to the first invention, the light transmitted throughtransparent film or phase shifting groove and the light transmittedthrough the portion where these are not provided interfere with eachother at the boundary area of transmission and light shield regions soas to weaken themselves in each of transmission regions at the time ofexposure. Thus, the bleeding of contour of an image projected on a wafercan be reduced so that the contrast of the projected image is improvedconsiderably resulting in a remarkable improvement of the resolution anddepth of focus. Especially, in this case, the phase contrast isgenerated within the lights being transmitted through one transmissionregion. Therefore, there is no restriction imposed upon the arrangementof transparent film no matter how complicated the pattern is on themask. Also, the arrangement of transparent film can be made withoutdifficulty no matter how narrow the pattern width is in the transmissionregion. As a result, the accuracy of pattern transfer will not belowered locally, making it possible to improve remarkably the transferaccuracy of the entire pattern formed on the mask.

According to the second invention, the manufacturing time of mask havinga means for shifting phase of light can be reduced considerably becausethere is no need for preparing specially any pattern data of transparentfilm or phase shifting groove.

According to the third invention, the light transmitted throughtransmission region and the light transmitted through groove and phaseshifting groove interfere with each other to weaken themselves at theend portion of the transmission region so that the bleeding of contourof a image projected on a wafer can be reduced, and the contrast of theprojected image will be improved considerably, making it possible toimprove the resolution and depth of focus remarkable. As a result, theaccuray of pattern transfer can be improved.

According to the fourth invention, the light intensity at the corners oftransmission region is increased by arranging sub-transmission regionsat the corners of transmission region so that not only the resolution ofthe projected image at each side but also the resolution of the cornersthereof can be improved.

What is claimed is:
 1. An integrated circuit device projection exposuremethod for transferring a circuit pattern, on a first major surface of atransparent mask substrate, onto a photoresist film on an integratedcircuit wafer through an optical projection system, the methodcomprising:(a) mounting the mask substrate on a first position in theprojection system, the circuit pattern having a first light transmissionregion and a second light transmission region for substantiallyreversing the phase of a transmitted light without substantiallyattenuating the amplitude of the transmitted light relative to the firstlight transmission region, which second light transmission regionsubstantially borders on and is adjacent to the first light transmissionregion to the extent that destructive interference between light beamsfrom both vicinity sides of a boundary between the second lighttransmission region and the first light transmission region sufficientlytakes place such that resolution is improved; (b) mounting the waferhaving the resist film onto a second position in the projection system;(c) exposing the mask substrate mounted on the first position to anexposure light beam having a predetermined wavelength, and having thelight beam transmit through the mask substrate in such manner that thephase of a transmitted light beam through the first light transmissionregion is reversed, as compared to that of a transmitted light beamthrough the second light transmission region, by a first phase-shiftingstructure disposed at one of the first and second light transmissionregions; (d) focusing the transmitted light beams through the projectionsystem so as to form a real image of the circuit pattern, on the masksubstrate, onto the resist film on the wafer in such manner that an edgeportion of the real image is made clear on the second light transmissionregion side of the first light transmission region due to destructiveinterference between light beams from both vicinity sides of a boundarybetween the first and second light transmission regions, and exposingthe wafer mounted on the second position in the projection system to thefocused light beams; and (e) transferring the circuit pattern, on themask substrate, onto the resist film on the wafer through the projectionsystem.
 2. An integrated circuit device projection exposure methodaccording to claim 1, wherein the projection system is an opticalreduction projection system.
 3. An integrated circuit device projectionexposure method according to claim 2, wherein the first phase-shiftingstructure is a first transparent film having a predetermined thicknessdisposed on a substantially entire surface of one of the first andsecond light transmission regions.
 4. An integrated circuit deviceprojection exposure method according to claim 1, wherein said firstphase-shifting structure is disposed on one of the first and secondlight transmission regions.
 5. An integrated circuit device projectionexposure method according to claim 1, wherein said first phase-shiftingstructure is disposed in one of the first and second light transmissionregions.
 6. An integrated circuit device projection exposure methodaccording to claim 1, wherein the second light transmission regionborders on the first light transmission region, and a width of thesecond light transmission region is sufficiently narrow so as not toform an independent bright real image corresponding thereto onto thephotoresist film.
 7. An integrated circuit device projection exposuremethod according to claim 6, wherein the first phase-shifting structureis a first transparent film having a predetermined thickness disposed ona substantially entire surface of one of the first and second lighttransmission regions.
 8. An integrated circuit device projectionexposure method according to claim 7, wherein the first transparent filmis formed directly on the first major surface of the transparent masksubstrate.
 9. An integrated circuit device projection exposure methodaccording to claim 8, wherein the first major surface of the transparentmask substrate is exposed over the entire surface of the other of thefirst and second light transmission regions.
 10. An integrated circuitdevice projection exposure method according to claim 7, wherein thefirst transparent film is disposed on the first light transmissionregion.
 11. An integrated circuit device projection exposure methodaccording to claim 7, wherein the first transparent film is disposed onthe second light transmission region.
 12. An integrated circuit deviceprojection exposure method according to claim 11, wherein the projectionsystem is an optical reduction projection system.
 13. An integratedcircuit device projection exposure method according to claim 11, whereinthe projection system is an optical reduction projection system.
 14. Anintegrated circuit device projection exposure method according to claim6, the circuit pattern further having:a first light shield region forshielding the exposure light beam, disposed at a side of the secondlight transmission region opposite a side thereof at which the firstlight transmission region is disposed, and bordering on the second lighttransmission region.
 15. An integrated circuit device projectionexposure method according to claim 14, wherein the first phase-shiftingstructure is a first transparent film having a predetermined thicknessdisposed on a substantially entire surface of one of the first andsecond light transmission regions.
 16. An integrated circuit deviceprojection exposure method according to claim 15, wherein the firsttransparent film is disposed on the first light transmission region. 17.An integrated circuit device projection exposure method according toclaim 16, the circuit pattern further having:a second light shieldregion for shielding the exposure light beam, disposed at a side of thefirst light transmission region opposite a side thereof at which thefirst light shield region is disposed, and adjacent to the first lighttransmission region; and a third light transmission region disposedbetween and bordering on both the second light shield region and thefirst light transmission region, wherein a phase of the transmittedexposure light beam transmitted through the third light transmissionregion is substantially reversed as compared with the phase of thetransmitted exposure light beam transmitted through the first lighttransmission region, by the first phase-shifting structure, so as tomake an edge portion of the real image clear on the third lighttransmission region side of the first light transmission region, andwherein a width of the third light transmission region is sufficientlynarrow so as not to form an independent bright real image thereof on thephotoresist film.
 18. An integrated circuit device projection exposuremethod according to claim 16, the circuit pattern further having:afourth light transmission region, disposed at a side of the first lightshield region opposite a side thereof at which the first lighttransmission region is disposed; and a fifth light transmission regionnarrower than the fourth light transmission region and disposed betweenand bordering on both the first light shield region and the fourth lighttransmission region, wherein the mask has a second phase-shiftingstructure for substantially reversing a phase of the transmittedexposure light beam transmitted through the fifth light transmissionregion as compared with a phase of the transmitted exposure light beamtransmitted through the fourth light transmission region, so as to makean edge portion of the real image clear on the fifth light transmissionregion side of the fourth light transmission region, wherein the secondphase-shifting structure includes a transparent film on substantially anentire surface of the fourth light transmission region, and wherein awidth of the fifth light transmission region is sufficiently narrow soas not to form an independent bright real image thereof on thephotoresist film.
 19. An integrated circuit device projection exposuremethod according to claim 15, wherein the first transparent film isdisposed on the second light transmission region.
 20. An integratedcircuit device projection exposure method according to claim 19, thecircuit pattern further having:a fourth light transmission region,disposed at a side of the first light shield region opposite a sidethereof at which the first light transmission region is disposed; and afifth light transmission region narrower than the fourth lighttransmission region and disposed between and bordering on both the firstlight shield region and the fourth light transmission region, whereinthe mask has a second phase-shifting structure for substantiallyreversing a phase of the transmitted exposure light beam transmittedthrough the fifth light transmission region as compared with a phase ofthe transmitted exposure light beam transmitted through the fourthlight-transmission region, so as to make an edge portion of the realimage clear on the fifth light transmission region side of the fourthlight transmission region, wherein the second phase-shifting structureincludes a second transparent film on substantially an entire surface ofthe fourth light transmission region, and wherein a width of the fifthlight transmission region is sufficiently narrow so as not to form anindependent bright real image thereof on the photoresist film.
 21. Anintegrated circuit device projection exposure method according to claim20, wherein the first and second transparent films constitute a singletransparent film connected with each other within the first light shieldregion.
 22. An integrated circuit device projection exposure methodaccording to claim 21, wherein the first and second transparent filmsrespectively contact the first major surface of the mask substratewithin substantially an entire surface of the second and fifth lighttransmission regions.
 23. An integrated circuit device projectionexposure method according to claim 19, the circuit pattern furtherhaving:a second light shield region for shielding the exposure lightbeam, disposed at a side of the first light transmission region oppositea side thereof at which the first light shield region is disposed, andadjacent to the first light transmission region; and a third lighttransmission region disposed between and bordering on both the secondlight shield region and the first light transmission region, wherein themask has a third phase-shifting structure for substantially reversingthe phase of the transmitted exposure light beam transmitted through thethird light transmission region as compared with the phase of thetransmitted exposure light beam transmitted through the first lighttransmission region, so as to make an edge portion of the real imageclear on the third light transmission region side of the first lighttransmission region, wherein the third phase-shifting structure includesa third transparent film on substantially an entire surface of the thirdlight transmission region, and wherein a width of the third lighttransmission region is sufficiently narrow so as not to form anindependent bright real image thereof on the photoresist film.
 24. Anintegrated circuit device projection exposure method according to claim19, wherein the projection system is an optical reduction projectionsystem.